1. Field of the Invention
This invention relates to a potentially economically viable method for the preparation of hydrogen peroxide in deep eutectic solvents and its use in the destruction of hazardous chemicals.
2. Background of the Related Art
The invention relates to the production of hydrogen peroxide, a material of commercial importance, which is used in large volumes for bleaching and chemical oxidations. Customary industrial processes for preparing hydrogen peroxide are the electrolysis of acidic ammonium sulfate solutions, the oxidation of isopropyl alcohol and the anthraquinone process. The direct synthesis of hydrogen peroxide from the elements over transition metal catalysts is known, but has not found commercial use to date. There are several reasons for this. For instance, hydrogen and oxygen form explosive gas mixtures if the level of hydrogen in the gas mixture is above 5% by volume. On the other hand, the rate of formation of hydrogen peroxide on using hydrogen-oxygen mixtures outside the explosive range is generally too low to ensure reasonable space-time yields. In addition, an excessively high level of oxygen in the reaction gas can speed up the oxidative degradation of the catalysts. The most common process for production of hydrogen peroxide is the anthraquinone autoxidation process involving alternate hydrogenation and oxidation of one or more anthraquinones or tetrahydro anthraquinones, usually alkyl anthraquinone or alkyl tetrahydro anthraquinone, in a working solution composed of a mixture of organic solvents. The hydrogen peroxide formed is usually recovered by extraction with water to form an aqueous solution. The process is described extensively in the literature, for example in Kirk-Othmer, “Encyclopedia of Chemical Technology”, Vol. 13, “Hydrogen Peroxide”, Online Posting Date Aug. 17, 2001.
The anthraquinone autoxidation process is very efficient but it is difficult to avoid impurities from the working solution to be extracted together with the hydrogen peroxide. Further, concentrating the aqueous solution of hydrogen peroxide by for example evaporation is energy consuming and accumulates impurities with low volatility, and purification by distillation requires even more energy.
U.S. Pat. No. 7,195,748 disclosed a process for the production of hydrogen peroxide by the anthraquinone process, comprising a hydrogenation stage, an oxidation stage and an extraction stage. According to the invention, catalytic hydrogenation of anthraquinone derivatives dissolved in a working solution is carried out in the presence of added molecular oxygen.
U.S. Pat. No. 3,761,580 discloses production of very pure aqueous hydrogen peroxide solutions by stripping of hydrogen peroxide from the working solution, condensing the resulting vapors containing a mixture of hydrogen peroxide and organic solvents and extracting the condensed vapors to give an aqueous hydrogen peroxide solution.
U.S. Pat. No. 4,824,609 discloses purification of working solution by extraction with carbon dioxide, while U.S. Pat. No. 4,668,436 discloses purification by extraction with a non-cyclic hydrocarbon. Purification of hydrocarbon fluids by extraction with various ionic liquids has been disclosed in, for example, WO 01/40150 and S. Zhang et al, “Extractive Desulfurization and Denitrogenation of Fuels Using Ionic Liquids”, Ind. Eng. Chem. Res. 2004, 43, op. 614-622. M. Seiler et al, “Hyperbranched polymers: new selective solvents for extractive distillation and solvent extraction”, Separation and Purification Technology 30 (2003) 179-197, discloses use of hyper branched polymers for extractive distillation and solvent extraction.
U.S. Pat. No. 7,157,071 discloses a process for the production of hydrogen peroxide from hydrazine hydrate or hydrazine salt, represented by a general formula: N2H4nX, wherein, X is H2O, H2SO4, HNO3, HCl, HBr, HI or CH3COOH; n is 0.5, 1 or 2; N is nitrogen; H is hydrogen; S is sulfur; Cl is chlorine; Br is bromine; and I is iodine, by its liquid phase oxidation with oxygen, using a solid catalyst comprising palladium but with or without halogen promoter, in an aqueous reaction medium with or without comprising a mineral acid and/or halide anions, U.S. Pat. No. 7,144,565 disclosed a process for the direct catalytic production of aqueous solutions of hydrogen peroxide from hydrogen and oxygen in the presence of a small amount of one or more water soluble organic additives (about 0.1-10% by weight). Suitable catalysts include nanometer-sized noble metal catalytic crystal particles. The catalyst particles preferably have a controlled surface coordination number of two to increase the selectivity of hydrogen peroxide production. The water-soluble additive(s) increases catalytic activity causing significant increases in the apparent first order reaction rate-constant for the direct production of aqueous hydrogen peroxide.
U.S. Pat. No. 7,105,142 described a process for the production of hydrogen peroxide from hydrogen and oxygen in a reaction solvent containing a halogenated promoter and/or an acid promoter, in the presence of a heterogeneous catalyst based on one or more metals of the platinum group, wherein the reaction solvent consists of: (1) an alcohol or mixture of alcohols; (2) an aliphatic ether having general formula (I); and (3) optionally water. The solvent mixture may also contain one or more C5-C32 hydrocarbons. The process operates under high safety conditions with a high productivity and molar selectivity towards the formation of H2O2. The methods described above for generating hydrogen peroxide suffer from several disadvantages and are not appropriate for all applications. Consequently, other methods for generating hydrogen peroxide are desired.
Superoxide is a reactive oxygen species formed by the one electron reduction of oxygen, has a longer life time than singlet oxygen and is capable of decolorizing (bleaching) stains and killing bacteria. Throughout this application, superoxide is represented as O2.− based on common literature practice.
U.S. Pat. No. 5,663,475 disclosed a method and reactor for oxidation of petrochemicals using ozone and hydrogen peroxide as a replacement for the incinerator that is usually used.
Superoxide is very reactive in aqueous solutions and protic solvents. The rate constant for O2.− reaction with H2O is 1×107/mol/sec (Sawyer, et al., 1981). On the other hand, O2.− is quite stable in aprotic solvents. In general, O2.− behaves as an oxidant, and as a strong nucleophile, depending on the solvent, in particular on the pH or presence of an easily abstractable hydrogen atom. Superoxide also acts as a one-electron reductant of metal ions and complexes.
Superoxide ion has been known by chemists as long as 1934 when Haber and Weiss (Haber, F. and Weiss, J. Proc. R. Soc., 1934, A147, 332) have proposed that O2.− is formed in the decomposition of hydrogen peroxide and in the oxidation of ferrous ions by dioxygen in aqueous solutions. Sawyer and co-workers (Merritt, M. V. and Sawyer, D. T. J. Org. Chem. 1970, 35, 2157. Sugimoto, H.; Matsumoto, S.; and Sawyer, D. T. Environ. Sci. Technol., 1988, 22, 1182.)
pioneered work on superoxide ion, particularly the direct electrochemical reduction of dissolved oxygen gas in aprotic solvents to form O2.− according to the following reactionO2+e−→O2.−  (1)
A comprehensive review of superoxide ion chemistry is given by Sawyer et al. (Sawyer, D. T., Sobkowiaand, A. k, and Roberts, J. L. Electrochemistry for Chemists, 2nd ed., chapter 9, Wiley Interscience: New York, 1995.). Superoxide ion can be formed directly from solvation of KO2 in aprotic solvents, or electrochemically via direct cathodic reduction of dioxygen (typically E=−1.0V vs SCE). O2.− is a strong nucleophile and disproportionates in water to O2 and hydroperoxide:2 O2.−+H2O→O2+HOO−+HO−  (2)
To avoid this reaction, generation and utilization of O2.− must be done in aprotic solvents. Acetonitrile (MeCN), dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) are commonly used. Che et al. (Che, Y.; Tsushima, M.; Matsumoto, F.; Okajima, T.; Tokuda, K.; and Ohsaka, T. J. Phys. Chem. 1996, 100, 20134.) studied the water-induced disproportionation of the electrogenerated superoxide ion in MeCN, DMF, and DMSO media containing various concentrations of water using UV-vis spectroscopy. In dipolar aprotic solvents superoxide ion is quite stable, because disproportionation to give the peroxide dianion (O22−) is highly unfavorable (Sawyer, D. T. Oxygen Chemistry; Oxford University Press: New York, 1991. Afanas'ev, I. B. Superoxide Ion: Chemistry and Biological Implications; CRC Press: Boca Raton, Fla., 1989; Vol. 1). However, the addition of acidic substrates (HA), which act as a Brønsted acid, to stable solutions of O2.− in aprotic solvents accelerates the disproportionation, depending on the protic strength (acidity) of HA.
Tang et al. (Chem. Comm., 1345-1347 (2005)) described a method for the electrosynthesis of hydrogen peroxide in an ionic liquid and an in situ epoxidation of alkenes using the generated H2O2.
A deep eutectic solvent (DES) is a type of ionic solvent with special properties composed of a mixture which forms a eutectic with a melting point much lower than either of the individual components. The first generation eutectic solvents were based on mixtures of quaternary ammonium salts with hydrogen donors such as amines and carboxylic acids. The deep eutectic phenomenon was first described in 2003 for a 1 to 2 by mole mixture of choline chloride (2-hydroxyethyl-trimethylammonium chloride) and urea. Choline chloride has a melting point of 302° C. and that of urea is 133° C. The eutectic mixture however melts as low as 12° C.
This DES is able to dissolve many metal salts like lithium chloride (solubility 2.5 mol/L) and copper(II) oxide (solubility 0.12 mol/L). In this capacity, these solvents could be applied in metal cleaning for electroplating. Because the solvent is conductive, it also has a potential application in electropolishing. Organic compounds such as benzoic acid (solubility 0.82 mol/L) also have great solubility and this even includes cellulose (filtration paper). Compared to ordinary solvents, eutectic solvents also have a very low VOC and are non-flammable.
Other deep eutectic solvents of choline chloride are formed with malonic acid at 0° C., phenol at −40° C. and glycerol at −35° C.
Compared to ionic liquids that share many charactistics but are ionic compounds and not ionic mixtures, deep eutectic solvents are cheaper to make, much less toxic and sometimes biodegradable.
WO 2002 026381 disclosed an invention related to DES and methods for their preparation. In particular, the invention relates to ionic compounds comprising hydrated metal salts, which are liquid at low temperatures, generally below about 100° C.
WO 02/26701 A2 disclosed a method for the synthesis of DES compounds with a freezing point of up to 100° C. by the reaction of one amine salt (I), such as choline chloride with an organic compound (II) capable of forming a hydrogen bond with the anion of the amine salt, such as urea, wherein the molar ratio of I to II is from 1:1.5 to 1:2.5. The DES compounds are useful as solvents, and electrolytes for example in electroplating, electrowinning, electropolishing, and as catalysts.
WO 00/56700 disclosed a method for the synthesis of DES having a melting point of no more than 60° C., formed by the reaction of a quaternary ammonium compound or a mixture of two or more thereof; with a halide of zinc, tin or iron, or a mixture of two or more thereof.
We were the first to show that a stable superoxide ion can be generated in ILs [AlNashef et al. Ph. D. Dissertation, 2004]. We also showed that hexachlorobenzene could be destroyed by the reaction of the superoxide ion generated in selected ILs. However, the superoxide ion reacted with the cation of the IL wasting part of the solvent and producing undesired byproducts and hence, reducing the efficiency of the process.
U.S. Pat. No. 5,663,475 disclosed a method and reactor for oxidation of petrochemicals using ozone and hydrogen peroxide as a replacement for the incinerator that is usually used.
From what was mentioned above it is clear that there is a need for a viable method for the production of hydrogen peroxide that is inexpensive, occurs at ambient temperature, and most importantly, benign.